My Eyedropper has suddenly started changing all samples to white. No matter what area of an image I click it samples white, this is regardless of sample size or modifier keys. If I manually select a color with the Color Picker, and then sample an area of the image with the Eyedropper, same result, white. All of my other tools are working correctly. I tried resetting the tools, I verified my documents settings are correct, I restarted Photoshop, restarted the computer...nothing.

It corrected itself after I selected and used the Measuring Tool, which shares a space with the Eyedropper on the Tools palette. If anyone has additional info to add then please do so. If not I'll answer it myself, or we can flag it for closing. Weirdest bug I've ever experienced.
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user4204Apr 4 '12 at 23:47

what was wrong with the way eyedropper worked in previous version? where is quick mask mode? what is it? why are these new features getting in my way?
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user1043568Nov 5 '13 at 13:35

It's tough to answer with any certainty since you yourself aren't sure and now the problem is resolved.

If this happened in only 1 photoshop file, it's very likely that you had a layer mask selected instead of the image layer. If this were the case, your eyedropper would be selecting the mask values (and if the mask wasn't actually masking anything out, it would be all white).